276 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



above this floor; one point, Half Dome, reaching an eleva- 

 tion of 8,927 feet. While the valley is a portion of the 

 canyon of the Merced River, it finds its natural continua- 

 tion up-stream in the canyon of Tenaya Creek rather than 

 in that of the Merced, which enters the valley at right 

 angles to its general trend. This is brought out by a view 

 (PL XXXI) which shows the east end of the valley and 

 Tenaya Canyon beyond. Any one regarding the valley 

 from a high point can hardly fail to be struck with the great 

 size of Tenaya Canyon. The present Tenaya Creek 

 appears to be entirely inadequate to the work it seems to 

 have performed, even after allowing liberally for enlarge- 

 ment by the glacier that formerly occupied it. 



Tenaya Creek finds its source in Lake Tenaya. The 

 basin of this lake is separated by a low pass from that of 

 Tuolumne Meadows. It has been suggested by Mr. Solo- 

 mons, of the Sierra Club, that the upper part of Tuolumne 

 River at one time flowed south through this pass into Ten- 

 aya Lake, thence finding its way into Tenaya Canyon, the 

 great size of which may thus be accounted for. The plaus- 

 ibility of this is enhanced when we note that the present 

 Tuolumne, for some miles west of Tuolumne Meadows, 

 flows down in a series of cascades and appears to be cut- 

 ting a new canyon. There is thus apparent evidence that 

 the Tuolumne has captured the upper portion of the hypo- 

 thetical former North Fork of the Merced River or the pres- 

 ent Lyell Fork of the Tuolumne and its branches. An objec- 

 tion to this hypothesis, which is perhaps fatal, is found in 

 the discovery, before noted, of a channel representing the 

 Neocene Tuolumne River somewhat to the north of the 

 present canyon of the Tuolumne. The pebbles of this 

 Neocene river deposit consist largely of the slates and 

 schists of the Mount Dana sedimentary area, showing that 

 the Neocene Tuolumne River headed as it now does in the 

 neighborhood of Tuolumne Meadows.^ It would seem 



1 The slates and tuffs of the Mt. Dana belt are continued to the northwest, but there 

 lie on the east slope of the Sierra Nevada, so that the slate and schist pebbles referred 

 to could hardly have come from any other part of this belt, except as indicated from the 

 head of the present Tuolumne drainage, that is, from Mt. Dana and vicinity. 



